Tentacle gets out of mesh
To me, your bone chain is inverted.

You can remark that when you move the bottom bone, all come with it, but when you take the top bone it is constrained by the bottom bone :



So you can simply invert the situation (apply rotations and scale to your mesh before that). I have separated a tentacle in order you see well :


Select the armature
Go to edit mode
Select all the bones
And rotate it 180°
Adjust the Z location
Go back to object mode
Reparent the tentacle




For a more complete model, add another "top parent bone". This will allow to bring all your tentacles together and also the jelly body.



The blend file :